Materials Science

Hardening Hydrogels

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Science  04 Aug 2006:
Vol. 313, Issue 5787, pp. 592-593
DOI: 10.1126/science.313.5787.592d

In recent years, preparation methods for biocompatible bonelike materials have grown increasingly sophisticated. One approach has been to mineralize polymeric hydrogels by the addition of calcium salts; however, the chemical functionality of such systems is not easily tuned, nor is the polymer template easily disassembled after mineralization. Schnepp et al. replace the polymer with a supramolecular network that self-assembles from water-soluble small-molecule building blocks. They start with an aqueous solution of tyrosine phosphate, N-substituted by an aromatic fluorenylmethyloxycarbonyl (FMOC) group. Enzymatic dephosphorylation induces the assembly of gels composed of nanofilaments held together by tyrosine H-bonding and fluorenyl π-stacking interactions. By exposing the gels to different calcium ion concentrations for different periods of time, the authors achieve controlled degrees of calcium phosphate mineralization.

Nucleation of calcium phosphate along the fibers produced viscoelastic hybrid gels with enhanced thermal stability and stiffness. Furthermore, the shear threshold for a nonlinear response increased by two orders of magnitude relative to the unmineralized sample. Weeklong exposure to moderately concentrated CaCl2 led to extensively mineralized composites without disrupting the viscoelastic properties of the supramolecular structure; the organic material could then be removed by washing to produce macroporous networks. — MSL

Adv. Mater. 18, 1869 (2006).

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